1. Field of the Invention
The present invention relates to a letter printing system including a data processing unit, which receives an instruction to print document data containing letter data of a plurality of letters, generates print data from the document data and outputs the print data to a printing unit, and the printing unit, which performs printing on a paper sheet for envelope and a paper sheet for enclosure according to the print data inputted from the data processing unit and outputs the paper sheets in the order of printing.
2. Description of the Related Art
In recent years, letter producing systems are known. Such a letter producing system receives an instruction to print letter data, which is generated on a computer with an application program, such as Microsoft Word®, then, a printing unit of the system performs printing on a paper sheet for envelope and a paper sheet for enclosure, and an inserting and sealing unit of the system forms an envelope from the printed paper sheet for envelope and inserting and sealing the printed paper sheet for enclosure in the formed envelope, thereby producing a letter.
In a case where the inserting and sealing unit of the letter producing system is configured, for example, to automatically feed the paper sheets for one letter outputted from the printing unit in the order of output, recognize the first-fed paper sheet as a paper sheet for enclosure and the last-fed paper sheet as a paper sheet for envelope, form an envelope by folding the paper sheet recognized as the paper sheet for envelope, and insert and seal the paper sheet recognized as the paper sheet for enclosure in the formed envelope to produce a letter, it is necessary that the printing unit performs printing on the paper sheet for enclosure before printing on the paper sheet for envelope. However, letter data to be printed is usually generated without considering the order of printing to accommodate to the above-described inserting and sealing operation, and the order of page data for envelope and page data for enclosure forming the letter data often does not correspond to the order of printing accommodating to the inserting and sealing operation.
In order to address this problem, Japanese Unexamined Patent Publication No. 2002-225379 (hereinafter, Patent Document 1) proposes a method that allows printing page data in a predetermined order that is different from the order of the page data generated with an application program. In this method, when an instruction to print document data formed by pieces of page data is received, a printer driver once spools all the pieces of page data forming the document data sent from the application program and performs necessary sorting on the entire spooled data, and outputs the sorted data to the printing unit.